salience network is important for monitoring critical external events as well as internal states. As will be described throughout this text, psychopathological disorders such as schizophrenia, depression, anxiety, dementia, and autism have been shown to involve problems in turning networks on or off as well as problems in the connections within the network itself.
The historical considerations of psychopathology emphasized careful observation and interaction with the afflicted individuals as important methods for understanding the nature of the disorder. However, with progress in the neurosciences, brain imaging, and genetics, other levels of analysis have become possible. The new levels offer different perspectives for the field of mental illness, but because many of these discoveries are so new, it is not surprising that our understanding of the field of mental illness is currently in flux. Neuroscience research has been used to find more objective markers in the diagnosis and treatment of mental disorders. It has also helped describe cognitive, emotional, and motor processes in both health and illness. This has resulted in a better articulation of what underlies these processes such as problems in setting goals, having relationships with others, thinking, and feeling, as well as deficits in the memory system and the reward system.
What Is the Brain’s Default (Intrinsic) Network?
What does your brain do when you are just sitting and waiting or daydreaming or talking to yourself? This is a question that is just now beginning to be explored. In psychology, most of the research you read about involves a person doing something. Reacting to emotional pictures or solving cognitive problems are common examples. In these cases, one’s attention is focused on a task in the external world.
In the same way that the brain is organized to process spatial and verbal material differently and involve different cortical networks, it also appears that different circuits are involved with internal versus external information. A variety of studies have examined brain imaging procedures in which individuals performed internal tasks versus external tasks (e.g., Ray & Cole, 1985).
However, we all know that even without an external task to do, our mind is constantly working. It jumps from one thought to another. The psychologist William James called this process the stream of consciousness. Recent researchers refer to this process as mind wandering.
Those neural networks that are active during internal processing have come to be referred to as the brain’s default or intrinsic network (Buckner, Andrews-Hanna, & Schacter, 2008; Raichle, 2011; Raichle & Snyder, 2007). It has been suggested that intrinsic is a better term than default, since a variety of internal tasks use this network (C. Kelly, Biswal, Craddock, Castellanos, & Milham, 2012). The default network is separate from, but one that can be understood as similar to, other networks such as those involved in visual perception or motor activities. It is made up of a set of interacting brain regions. Those areas involved are pictured in Figure 2.23 and represent periods of brain imaging when individuals are not engaged in any active task.
default or intrinsic network: neural network that is active during internal processing
executive functions: cognitive functions involved in planning, understanding new situations, and cognitive flexibility
Figure 2.23 The Brain’s Default Network
Source: James King-Holmes/Henry Luckhoo/Science Source
Overall, the default network is involved during internal or private considerations that do not require processing external sensory information. In fact, it appears as if there is a negative correlation between activities in the default network versus networks associated with processing information from the environment. That is, when someone begins some cognitive activity, then new networks associated with that task become active and the default network becomes less active. This suggests that separate brain mechanisms evolved for dealing with information involving the external environment as opposed to considerations internal to the person. A variety of psychopathology disorders show problems with the default network in terms of being able to turn it off and engage in a more active external task. People with schizophrenia are one group that has difficulty turning off the default network and moving to an active task that uses a different network.
Different Networks Are Involved in Different Tasks
In addition to the default network, the executive and salience networks are dysfunctional in different psychopathologies (Menon, 2011). The central executive network is involved in performing such tasks as planning, goal setting, directing attention, performing, inhibiting the management of actions, and the coding of representations in working memory (Eisenberg & Berman, 2010). These are sometimes referred to as frontal lobe tasks, since damage to the frontal areas of the brain compromises performance of these tasks. These tasks are also referred to as executive functions, because they assist in planning, understanding new situations, and having cognitive flexibility. The salience network, as the name implies, is involved in monitoring and noting important (i.e., salient) changes in biological and cognitive systems.
The three networks—default, executive, and salience—show deficits in individuals with specific psychopathologies. Menon (2011) has reviewed the research literature and suggests that these networks play a prominent role in schizophrenia, depression, anxiety, dementia, and autism. As you will see throughout this book, the role of these networks may be dysfunctional in the network itself or in the ability to activate or deactivate specific networks in changing situations.
Figure 2.24 shows those areas of the brain that Menon (2011) found to be associated with each of these networks. The figure shows an MRI structural image of the brain in black and white. The areas that are activated during the task are displayed in color. The brain is shown in terms of a three-dimensional image along an x-, y-, and z-axis. The x-axis shows the brain from the side, the y-axis from the back; and the z-axis from above. The numbers below the image represent the location along each axis. Using these three numbers, brain imaging programs can identify the areas in relation to traditional anatomical structures.
In Figure 2.24, the central executive network, which is involved in higher order cognitive and attentional demands including planning for the future and remembering concepts, is shown in blue. The salience network, which is important for monitoring critical external events and internal states, is shown in yellow. The default network, which is active during mind wandering and when the person is not engaged in active problem solving, is shown in red.
modularity: the concept that specific areas of the brain are dedicated to certain types of processing
Let’s take a moment to understand how researchers describe brain function in terms of networks. One important concept is modularity. Modularity describes how specific areas of the brain are dedicated to certain types of processing. For example, as discussed early in the chapter, we know that a particular part of the temporal lobe, the FFA, is involved in processing responses to the human face. fMRI measures, for example, would show greater brain activation in this area when observing the human face as opposed to nonhuman faces.
Another important concept is connectivity. This asks how different areas of the brain work together in specific conditions. To determine connectivity, researchers examine fMRI or EEG measures from a large number of locations throughout the brain. It is assumed that those areas whose activity is correlated are in some way working together.
Figure 2.24 Structural Image
